Ropes are well known and are widely used to carry tensile loads in a variety of applications. Generally, a rope is formed by: (1) twisting or braiding individual fibers together to form individual strands, and (2) twisting or braiding the individual strands together to form the rope. The rope is thus formed from multiple interwoven strands of multiple interwoven fibers. One type of rope is hollow-braided rope. Generally, a hollow-braided rope includes an even number of strands (such as twelve strands) braided together in a helical pattern with half of the strands braided clockwise and the other half braided counter-clockwise. A cavity or void exists within a hollow-braided rope along the hollow-braided rope's longitudinal axis.
Rope terminations (also called rope terminators) are also well known. Rope terminations are formed at the ends of a rope and: (1) ensure that the strands of the rope do not unravel, and (2) enable the rope to be connected to an appropriate device or apparatus, such as the piston of a pneumatic air vehicle launcher, a hook, a winch drum, a brake lever, a turnbuckle, and the like. Certain known rope terminations are formed using the rope itself in combination with one or more additional mechanical components, while other known rope terminations are formed using the rope itself without employing any additional mechanical components.
One known type of rope termination that is formed using the rope itself in combination with additional mechanical components is a cup-and-cone rope termination (also called a spike-and-socket rope termination or a barrel-and-spike rope termination). Generally, in a cup-and-cone rope termination, the strands and fibers of a portion of the rope are clamped between two mechanical components as a tensile force is applied. FIG. 1A shows a cross-sectional view of one known cup-and-cone rope termination 10 formed at an end of a rope 15. This known cup-and-cone rope termination 10 includes: (a) a rigid cone 20 including a tapered outer surface; and (b) a rigid cup 30 including a generally cylindrical outer surface and a tapered, frustoconical inner surface having a cone angle α and defining a tapered bore through the cup 30. The inner surface of the cup 30 forms a cone receiving cavity configured to receive the cone 20, as described below.
To form this known cup-and-cone rope termination 10, a manufacturer: (1) threads a tail of the rope 15 into the tapered bore of the cup 30 through the smaller diameter opening, threads the tail through the tapered bore of the cup 30, and threads the tail out of the tapered bore of the cup 30 through the larger diameter opening; (2) inserts the cone 20, pointed end first, inside the tail of the rope 15 until the strands and fibers of a portion of the rope substantially surround and cover the outer surface of the cone 20; and (3) applies a tensile force to the cup 30 toward the tail of the rope 15 to cause: (i) the cone 20 to be received in the cone receiving cavity of the cup 30, (ii) the strands and fibers of the of the portion of the rope 15 surrounding the cone 20 to be clamped between the outer surface of the cone 20 and the inner surface of the cup 30, and (iii) the cup 30 to be locked in place.
Known cup-and-cone rope terminations have a variety of disadvantages. One disadvantage is that the cup of a typical cup-and-cone rope termination is made of heavy, thick-walled material. Specifically, cup-and-cone rope terminations require relatively shallow cone angles (e.g., the cone angle α indicated in FIG. 1A) to ensure that the cup and the cone components sufficiently clamp the strands and fibers of the portion of the rope therebetween. Generally, the shallower the cone angle, the more securely the cup and cone clamp the strands and fibers of the rope therebetween.
However, this large clamping force comes at a cost. Specifically, the shallower cone angles transmit increased radial loads to the cup as a tensile force is applied, and this radial load creates hoop stress in the cup wall. The ratio of cup radial load to rope tensile force for typical cup-and-cone rope terminations is about 10:1. That is, with the cup pulling against the rope (as in a typical rope termination), a 1 pound tensile force causes the cup to experience about a 10 pound radial load. The radial load is carried via hoop tension field, the details of which depend on wall thickness details of the cup. Thus, to successfully carry the large radial loads, the cup is typically made of heavy, thick-walled material such as carbon steel or stainless steel. This renders the use of the cup-and-cone rope termination particularly problematic in applications in which a rope (and any rope termination formed therein) having low mass is desired, such as in aeronautical or fast/dynamic applications.
Over the past few decades, ropes made of strands having fibers made of lightweight, synthetic materials (such as SPECTRA® (SPECTRA® is owned by Honeywell International Inc.); KEVLAR® (KEVLAR® is owned by E. I. du Pont de Nemours and Company); and VECTRAN® (VECTRAN® is owned by Kuraray Co., Ltd.)) have replaced ropes made of strands having fibers made of heavier materials, such as steel, for many applications. Since these lightweight synthetic fibers are slipperier than traditional steel fibers, cup-and-cone rope terminations having even shallower cone angles must be used to ensure that these slippery rope fibers are properly clamped between the cup and the cone. The shallower cone angle requires the use of an even heavier, thicker-walled cup that can withstand the hoop stresses caused by the shallower cone angle and the corresponding larger radial load. The added wall thickness of this (typically steel) cup offsets much of the advantage gained by the use of the lightweight synthetic rope fibers.
Another disadvantage is that local abrasion occurs at the portion of the rope near the smaller diameter opening of the tapered bore of the cup as tensile forces are applied to and removed from the cup. The cyclical application and removal of tensile forces causes the strands and fibers of the portion of the rope near the smaller diameter opening of the tapered bore of the cup to stretch and scrape against the cone while moving into and out of the tapered bore of the cup. Thus, each time a tensile force is applied to or removed from the cup, the likelihood that the cup-and-cone rope termination will fail increases. This disadvantage is amplified when the rope has fibers made of a synthetic material (such as any of those listed above) because such synthetic material is typically less abrasion resistant than conventional materials (such as steel). Also, synthetic fibers tend to stretch more than steel fibers under load, and the additional stretch through the smaller diameter opening of the cup exacerbates fiber abrasion at that critical area.
One known type of rope termination that is formed using the rope itself without employing any mechanical components is a Brummel Eye Splice. Generally, a Brummel Eye Splice rope termination includes a double-braided portion of hollow-braided rope ending in a closed loop. The double-braided portion of the hollow-braided rope includes an outer braid portion and an inner braid portion concentric with and disposed within the outer braid portion. The Brummel Eye Splice rope termination takes advantage of the tension-contraction coupling of hollow-braided rope construction to provide the Brummel Eye Splice rope termination with sufficient strength. More specifically, as a tensile force is applied to the Brummel Eye Splice rope termination, the helical construction of the outer braid portion of the double-braided portion of the hollow-braided rope causes the outer braid portion to clamp onto the inner braid portion. FIG. 1B shows an example Brummel Eye Splice rope termination 60 formed at an end of a rope 50. The Brummel Eye Splice rope termination has a termination length 2LDB, part of which includes a double-braided portion of the rope.
The Brummel Eye Splice rope termination has certain disadvantages. The double-braided portion of the hollow-braided rope must be relatively long to ensure that the Brummel Eye Splice rope termination is sufficiently strong and will not fail when appropriate tensile forces are applied. This increases material costs (since the double-braided portion of the rope includes twice the rope as a single-braided portion of the rope) and increases the weight of the rope, which is particularly problematic in applications in which a rope having low mass is desired, such as in aeronautical or nautical applications.
This also increases the termination length of the Brummel Eye Splice rope termination. The relatively long termination length (caused by the relatively long double-braided portion) causes ropes terminated with Brummel Eye Splice rope terminations to have relatively small running length ratios, which is detrimental for certain applications. Running length ratio is the length of raw, unmodified rope divided by the termination length. Minimizing the termination length thus maximizes the running length ratio. For certain applications, such as a pneumatic launcher towrope application and a block and tackle rigging application, rope and rope termination configurations that maximize the running length ratio offer advantages over those that consume valuable running length on rope terminations. In other words, for a rope of a given length, ropes having rope terminations with shorter termination lengths have higher running length ratios and offer unique advantages for certain applications. The relatively small running length ratio of the Brummel Eye Splice rope termination thus renders it unsuitable for certain applications (such as those with space constraints).
Accordingly, there is a continuing need for new and improved rope terminations and rope termination forming systems that solve the above-described problems.